Sunderland striker Duncan Watmore may need a second operation on his injured knee after suffering discomfort on his return to light training, reports BBC Sport.

The England Under-21 international, who was ruled out for the rest of the season with anterior cruciate ligament damage in December last year, may now face a further spell on the sidelines.

He is due to see a specialist this week to discover whether or not further surgery is required.

Boss David Moyes said: "Duncan Watmore might be needing a little bit of work done on his knee. Obviously, he's not back, but he might be needing a little bit more surgery on his knee.

"He's been feeling it - he's been running a little bit - so he'll see the surgeon this week."